I don't know about it being the weirdest, but a recurring dream from my late teens to the early 20's has been seared into my memory that goes like this:

The way the dream starts varies, but a common version is me being asked to explore a staircase that was yet to be fully explored. Some versions has me go up, the others go down, and yet still others has me trying both. In some versions, I was sent with a team, the members of which succumbed to thirst, hunger, and fatigue as the expedition seemed to have no end. Sometimes, we (or I) discover that we've been going around “in circles” as we encounter the corpse of someone from our team who has earlier died, or I (in the versions I was alone) come across equipment I have abandoned way earlier.

In later versions, this has evolved into me (either starting with a team, but has since been whittled into just me) discovering an actual end to the staircase: a vast expanse of nothing but darkness. In there, I encounter some people (how they got there varies, some through the same staircase, the others through other means, and yet still others don't know how). I somehow convinced them to join me in exploring the darkness. To do this, we arranged ourselves in a circle, facing outwards with arms linked. That way, we wouldn't lose a person. We try to go off on a direction and explore the darkness that way. As we encounter more people willing to join us, they add themselves into the circular chain. It goes on and on, seemingly without end. The dark expanse just goes on and on forever.

In still later versions, this dark expanse is replaced by a huge subterranean cavern. Gone is the staircase, and I just dropped into the bottommost cavern. The same sequence of events as with the "dark expanse" version happens, but now, we can actually see where we're going and there's no need for forming a human circular chain.

In one late, and rare, version of this dream, we come across a well-lighted cavern whose center lies a shining stalagmite. We couldn't approach the stalagmite, however, and just made that as a reference point in further explorations.

This recurring dream has become more and more rare as I grew older. I sometimes wonder what it all means, and why the dream changed over time. It seemed to have to do with my mental state at that time, but some things didn't make sense. It's also quite coherent as dreams go, which is probably why I still remember it years after.